Azeotropic refrigerant composition of monochlorodifluoromethane and chloropentafluoroethane



Patented June 9, 1953 AZEOTROPIC REFRIGERAN T COMPOSITION O FMONOCHLORODIFLUORO M E T HANE AND CHLOROPENTAFLUOROETHAN E AnthonyFrancis Benning, Woodstown, N. J., as-

signor to E. I. du Pont de Nemours and Company, Wilmington, 'Del., acorporation of Dela- Ware No Drawing. Application March 2, 1951, SerialNo. 213,674

This invention relates to refrigerants and more particularly tofluorine-containing compounds and mixtures thereof which are useful asrefrigerants.

The mixed fluorine and chlorine derivatives of methane and ethane haveattained widespread use in the field of refrigeration as a result oftheir chemical inertness, their low specific volumes and the. wide rangeof boiling points which is available in the various members of theseries. Difiuorodichloromethane (B. P. 29.8 C.), fluorotrichloromethane(B. P. 233 0.), fluorodichloromethane (B. P. 8.9 C.) andtetrafiuorodichloroethane (B. P. 3.5 C.) are among the most commonlyused compounds of this type. Another valuable member of the series ismonochlorodifluoromethane, which boils at 40.8 C. and which makes itpossible to attain lower temperatures than can be reached with thecompounds mentioned above. Highly eificient apparatus designed to usethis material is in common use.

When apparatus designed to employ a particular refrigerant has beeninstalled, the need sometimes arises for greater refrigerating capacity.This may be obtained by the use of a refrigerant having a lower boilingpoint and consequently a higher vapor pressure at the temperatureattained by the gas prior to its being compressed and liquefied. Thecapacity of any given refrigeration compressor is roughly proportionalto the pressure of the gas at the suction side of the compressor. Sincethe compressor can handle a fixed volume of gas per unit of time, anincrease in the suction pressure means an increase in the number ofmoles of gas put through the compressor in a given time, An increase inthe number of moles means an in crease in the total amount of heatrequired to vaporize the liquid in the evaporator, and an increase inthe amount of heat that is removed from the refrigerated space. Ingeneral, other factors such as variations in the latent heat ofvaporization play a relatively minor part in determining the change incapacity of a given refrigerating apparatus which will result from thesubstitution of one refrigerant for another.

In a given apparatus, it is not possible to use a refrigerant having aboiling point too much lower than that for which the apparatus has beendesigned, as the power input becomes undesirably high and the compressormotor becomes overloaded.

In order to provide greater refrigerating capac- 2 Claims. (Cl. 252-67)2 r ity for installations designed for the use ofmonochlorodifiuo-ro-methane,- it is therefore desirable to employ a gaswhich may be liquefied a few degrees below the boiling point of thatmaterial. In this general boiling range, propane andpropylen are theonly pure compounds known having suitable properties and sufficientavailability for extensive use sis-refrigerants. Propane boils at 42 C.and propylene at -48 C. However, each of these compounds is flammable,and presents an explosion hazard caseor leakage.

The use of azeotropic mixtures of pure-materials as refrigerants isdisclosed in U. S. Patent No. 2,101,993 and elsewhere in the art. Suchmixtures have the advantage over other'gas mixtures that the vaporcomposition of the azeotrope is the same as the liquid composition withwhich it is in equilibrium. With non-azeotropi'cmixlow-boilingcompositions which are useful as refrigerating agents, and moreparticularly to provide an azeotropic mixture which is effective ingiving greater refrigerating capacity with apparatus designed for usewith monochlorodifiuoromethane.

I have discovered that mixtures of monochloro-- difiuoromethane andchloropentafluoroethane form an azeotrope boiling at approximately -45.6C., in which about 63 mol percent is monochlorodifluoromethane. Themixture is a highly useful refrigerant suitable for replacement ofmonochlorodifluoromethane in refrigeration equipment when a lowertemperature or greater capacity is desired. Its use results in 22%greater refrigerating capacity than is-obtained withmonochlorodifiuoromethane, other conditions being the same. This mixturehas the further advantage that only slight changes in the boiling pointoccur when the composition is varied over a considerable range on eitherside of the actual azeotropic composition. Mixtures containing between50 and mol percent monochlorodifluoromethane all boil between about 45.2and 45.6 C., so that there is little tendency for fractionation to takeplace with any of thesemixtures. They are all effective refrigeratingagents.

The boiling points of mixtures of monochlorodifluoromethane andchloropentafluoroethane were determined experimentally with thefollowing results:

M01 percent monochlorodifluoromethane It is apparent from these figuresthat a minimum-boiling azeotrope exists at approximately 63 mol percentmonochlorodifiuoromethane and that the change in boiling point betweenthe limits of 50 and '75 mol percent monochloro difiuoromethane is verysmall. The boiling point of mixtures containing 50 mol percent of eachcomponent will be seen to be approximately -45.2 C.

In preparing these mixtures, it is desirable that the components be atleast 99% pure and that they contain no appreciable amount of impuritieswhich are corrosive or which separate upon evaporation, so as tointerfere with the efiiciency of refrigeration. No special mixingprocedure need be followed, provided the proper relative amounts of thetwo components are used.

The compositions disclosed herein are chemically inert, non-inflammableand are essentially non-corrosive. They combine the valuablecharacteristics possessed generally by fluorochlorohydrocarbons with alow boiling .point which is of particular significance when lowtemperatures are to be attained or when extra capacity must a beobtained with existing refrigerating equipment.

These refrigerants may be used in domestic or commercial refrigeratorsand freezers, industrial cooling systems and air-conditioning systems,or in any other system in which cooling is effected by the evaporationand expansion of liquid refrigerant. In such systems, the expanded gasis compressed and condensed to a liquid, and is recycled to theexpansion device. Various specific types of refrigerating units forwhich the compositions here disclosed are of value are described inRefrigeration Fundamentals. 6th edition, 1949 (American Society ofRefrigerating Engineers).

Iclaim: v 1. A 1ow-boiling refrigerant composition whic consists of amixture of monochlorodifluoromethane and chloropentafluoroethane inwhich the mol percent of monochlorodifluoromethane 2. A low-boilingrefrigerant composition consisting of a mixture ofmonochlorodifluoromethane and chloropentafiuoroethane, in which the molpercent of monochlorodifluoromethane is between and 75.

ANTHONY FRANCIS BENNING.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,479,259 Reed et a1. Aug. 16, 1949 2,511,993 Reed June 20,1950 OTHER REFERENCES Kinetic Technical Bulletin-B2 FreonCompounds-Kin'etic Chemicals, Inc, Wilmington, De1.-l95011 pagepublication.

1. A LOW-BOILING REFRIGERANT COMPOSITION WHICH CONSISTS OF A MIXTURE OFMONOCHLORODIFLUOROMETHANE AND CHLOROPENTAFLUOROETHANE IN WHICH THE MOLPERCENT OF MONOCHLORODIFFUROMETHANE IS 63.